1. Field of the Invention
The present invention deals with hoppers and bins for the containment of granular material and, in particular, with coal containing hoppers which are mounted on larry cars for the purpose of charging coke ovens.
2. Description of the Prior Art
Coke ovens are conventionally provided with coal by means of larry cars which traverse the battery top on tracks and which transport a plurality of coal containing hoppers. These hoppers generally are open at their tops and have converging sides and a bottom discharge opening which may be closed by means of a sliding gate. The hoppers are also usually gravity operated so that when the larry car is positioned so that each of its hoppers is above a charging hole, the contents of these hoppers may be discharged by withdrawing their sliding gates from the bottom of their discharge openings. After a hopper has been emptied, however, it is important that its sliding gate be quickly closed so as to prevent the entry of coke oven gases through the discharge opening into the hopper interior. If substantial amounts of these gases do enter the interior of a hopper, they may condense on the hopper's interior walls so as to form tarry deposits which may impede the flow of coal from the hopper. It is also important that the sliding gate be closed in a timely manner to eliminate the possibility of discharging undue amounts of pollutants into the atmosphere and to prevent heat and flame damage to the hopper and other auxilliary equipment.
It has been the practice to rely on the larry car operator to make a determination as to when coal flow from a hopper had ceased and when to activate the sliding gate. Because, though, it is often difficult for an operator to determine when a hopper is actually empty, this method has not proven to be entirely satisfactory. Accordingly, various devices which make use of capacitance probes, paddle switches or pivoting plates which directly contact the coal have been suggested for the purpose of generating a signal to close the sliding gate at the precise moment that all of the coal has been fed from the hopper to the oven. Since, however, various disadvantages have been found to attend the use of some of these devices, it is the object of the present invention to provide a consistently reliable means of sensing the level of granular material in a hopper and, in particular, to detect when a hopper on a coke oven battery larry car is empty.